Milk when heated at temperatures in excess of 155.degree. F. for varying periods of time is known to acquire a "cooked flavor." Currently fluid milk is pasteurized or "ultra-pasteurized" by heat treatments of whole milk at temperatures ranging from 140.degree. to 165.degree. F. for periods of from 30 minutes to as low as 2 seconds. Such treatment is necessary to destroy disease-producing bacteria and check the activity of the fermentative bacteria found in raw whole milk. However, all bacteria in raw whole milk are not killed by such treatment and hence the milk has a limited shelf-life and must be refrigerated at temperatures near 4.degree. C. during all shipping, marketing and storing.
There are processes known for producing ultrahigh-temperature (UHT) sterilized milk. Such processes are described for example by H. Burton, Dairy Science Abst., 31, pages 287-297 (1969) aND T. R. Ashton, J. Soc. Dairy Tech., Vol. 18, No. 2 pp. 65-83 (1965). While UHT processing of milk has a slightly different meaning in the U.S. and Canada from that in Europe each involves treatment of milk at temperatures of at least 190.degree. F. for varying periods of time and generally at about 300.degree. F. for around 4 seconds. Unfortunately, milk when heat treated at such high temperatures (or even lower for more prolonged periods of time), develops an undesirable and unpalatable "cooked" flavor thus rendering the milk generally unmarketable, especially in the United States. Much research has been carried out to determine the nature of the "cooked" flavor and provide a means for its elimination. Both J. T. Hutton et al. J. of Dairy Science, 35 P. 699 (1952) and H. Burton, Proc. 15th International Dairy Congress 3, p. 1729 (1952) have speculated that the "cooked" flavor of heated milk is due to the liberation of sulfhydryl groups in the milk. Later work of Burton (Dairy Sci. Abstr., 31, p. 295-1969) as well as others has expressed doubts as to the significance of free sulfhydryl groups in milk.
Prior to the present invention there was no procedure know for removing the "cooked" flavor caused by the heating process of UHT-sterilized milk and other similarly treated milk. In some cases the intensity of the "cooked" flavor has been reduced, but not removed, by refrigeration.
In 1971, over 45 billion pounds of fluid milk were sold in the United States all of which required extensive refrigeration. While sterilization of fluid milk would have the obvious advantages of conserving energy and fuel requirements in processing, increasing product shelf-life, permitting shipping, marketing and storing at ambient temperatures, the presence of a "coooked" flavor currently associated with such milk renders it generally unmarketable.
I have now discovered that the "cooked" flavor associated with heat treated fluid milk can be removed according to my invention as described hereinbelow.
Accordingly, it is the primary object of my invention to provide a process whereby the "cooked" flavor attendant to heat treated fluid milk is removed.
It is a further object of my invention to provide a means for producing a marketable fluid milk which may be shipped, marketed and stored at ambient temperatures without deterioration and spoilage.
A still yet further object of the present invention is to provide a means whereby one may obtain fluid milk having a prolonged shelf-life without the necessity of refrigeration.
Yet another object of the invention is to provide a method of processing milk which will remain wholesome without refrigeration and possess a good flavor which to the average consumer can not be distinguished from freshly pasteurized homogenized milk.
These and other objects of the present invention will become apparent from the following discussion.